On my way over to a friend’s house last night, an unusual thing happened: a firefly which was in the process of lighting up got squashed against my windshield at that exact moment. While there wasn’t much resembling an insect left, smeared across the glass was a streak of glowing green goo which continued to fluoresce for 5 or 6 seconds before fading into black. In fact, in the last few moments the guts glowed brighter than the bug did.

Which got me thinking about 2 things. One, how do fireflies bioluminesce? And two, does science use this glowing protein in a similar way as GFP (green fluorescent protein, found in some jellyfish)?

Fireflies engage in a reaction in their nether-regions which involves an enzyme class called luciferase (Lucifer means “light bearer”). During these reactions light is produced by the oxidation of a luciferin pigment. This reaction happens very slowly, until the enzyme luciferase is present. The firefly adds additional oxygen through a tube called the abdominal trachea, and the reaction to light takes place. It happens in two steps (see wiki entry for more detail on intermediates).

This reaction is extremely efficient, considering that nearly all the energy in the reaction is converted to light (rather than being lost though many steps, or as heat, broken bonds, etc). When the firefly smashed on my windshield, essentially all the substrates present in the bug’s abdomen were exposed to the oxygenated air (oxygen being the only controlled ingredient). The reaction glowed brightly, but was spent quickly.

And, yes, science has found a way to make luciferase useful. It had been produced through genetic engineering, and luciferase genes can be inserted into cells or organisms to serve as a marker protein. Luciferase can be used, for example, to determine when red blood cells are breaking down in a blood bank, and no longer useful, or can indicate the levels of infection or a stage of a biological process.

Speaking as someone who’s caught a good number of them, there’s another interesting thing about fireflies, or as we called them, lightning bugs.

After you’ve handled one, or several, for a period of time, smell your hands. There’s a very pungent odor from them. To my way of thinking, since fireflies make themselves so visible, you can’t advertise yourself any better than lighting up in the dark, they’ve added something to make predators think twice about eating them.

If they don’t have the light, they don’t attract mates. If they don’t have the bad odor (and probably taste but I’m not going to test that one), predators will eat them before they can mate.